Fe-Co based target material and method for producing the same

ABSTRACT

There is disclosed a method for producing a Fe—Co based target material for forming a soft magnetic thin-film. This method comprises the steps of: preparing a first raw-material powder having an Fe:Co weight ratio ranging from 8:2 to 7:3 and a second raw-material powder having an Fe—Co weight ratio ranging from 2:8 to 0:10; mixing the first raw-material powder and the second raw-material powder together to obtain a powder mixture having an Fe:Co weight ratio ranging from 8:2 to 2:8; and applying a pressure of not less than 100 MPa to the powder mixture at a temperature ranging from 1073 to 1473 K for consolidation. At least one additional element selected from the group consisting of Nb, Zr, Ta and Hf is added to either one or both of the first and second raw-material powders in a total amount of 3 to 15 atom % with respect to the total amount of the powder mixture. The Fe—Co based target material thus produced has a high density, while having a magnetic permeability lower than the conventional one.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.128224/2006 filed on May 2, 2006, the entire disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

This invention relates to a Fe—Co based target material for forming asoft magnetic thin-film by a sputtering method, and a method forproducing the target material.

BACKGROUND ART

The recent progress in the magnetic recording technology is remarkable,and the record densities of magnetic record media are being heightenedfor increasing capacities of drives. In the magnetic record media forthe longitudinal magnetic recording systems currently used worldwide,however, an attempt to realize a high record density leads to refinedrecord bits, which require a high coercivity to such an extent thatrecording cannot be made with the record bits. In view of this, aperpendicular magnetic recording system is under study as a means ofsolving these problems and improving the record densities.

The perpendicular magnetic recording system is a system in which amagnetization-easy axis is oriented in the direction vertical to amedium surface in the magnetic film of the perpendicular magnetic recordmedium, and is suitable for high record densities. In addition, as forthe perpendicular magnetic recording system, a two-layered record mediumhas been developed having a magnetic record film layer where the recordsensitivity is improved and a soft magnetic film layer. A CoCrPt—SiO₂based alloy is generally used in the magnetic record film layer.

On the other hand, it is proposed that a soft magnetic film of a Fe—Co—Bbased alloy is used as a soft magnetic film of a two-layered recordmedium. For example, as disclosed in Japanese Patent Laid-OpenPublication No. 346423/2004, there is proposed a Fe—Co—B based alloytarget material in which the diameter of the maximum inscribed circlewhich can be drawn in a region with no boride phase in across-microstructure is equal to 30 μm or less.

Magnetron sputtering method is generally used for the preparation of theaforementioned soft magnetic film. This magnetron sputtering method is amethod in which a magnet is disposed behind a target material to leakthe magnetic flux onto a surface of the target material for convergingplasma in the leaked magnetic flux region, enabling a high-speedcoating. Since the magnetron sputtering method has a feature of leakingthe magnetic flux on the sputtering surface of the target material, inthe case where magnetic permeability of the target material itself ishigh, it is difficult to form, on the sputtering surface of the targetmaterial, the leaked magnetic flux necessary and sufficient for themagnetron sputtering method. In view of this, Japanese Patent Laid-OpenPublication No. 346423/2004 is proposed for a demand for reducing themagnetic permeability of the target material itself as much as possible.

On the other hand, the thickness of the target material can be increasedas the magnetic permeability of the target material is lowered. That is,a larger number of thin films can be produced from a single targetmaterial, resulting in an improved productivity. However, in theforegoing conventional technique, since the magnetic permeability is notsufficiently low, the maximum thickness of the target material is about5 mm. If the thickness exceeds 5 mm, leaked magnetic flux isinsufficiently created on the surface of the target material, causing aproblem that a magnetron sputtering cannot be performed normally.

DISCLOSURE OF THE INVENTION

The inventors have now found that a target material having a highdensity and a magnetic permeability lower than the conventional one canbe produced by mixing a first raw-material powder having a certain Fe:Coweight ratio and a second raw-material powder having another certainFe:Co weight ratio so that the resulting Fe:Co weight ratio becomesbetween 8:2 and 2:8, followed by hot-pressing the powder mixture intowhich a certain additional element of 3 to 15 atom % is added.

It is therefore an object of the present invention to provide an Fe—Cobased target material and a method for producing the Fe—Co based targetmaterial capable of ensuring a high density and lowering the magneticpermeability than conventional targets so that the thickness of thetarget material can be increased to improve productivity of thin-films.

The present invention provides a method for producing a Fe—Co basedtarget material, comprising the steps of:

preparing a first raw-material powder having an Fe:Co weight ratioranging from 8:2 to 7:3 and a second raw-material powder having an Fe—Coweight ratio ranging from 2:8 to 0:10;

mixing the first raw-material powder and the second raw-material powdertogether to obtain a powder mixture having an Fe:Co weight ratio rangingfrom 8:2 to 2:8; and

applying a pressure of not less than 100 MPa to the powder mixture at atemperature ranging from 1073 to 1473 K for consolidation,

wherein at least one additional element selected from the groupconsisting of Nb, Zr, Ta and Hf is added to either one or both of thefirst and second raw-material powders in a total amount of 3 to 15 atom% with respect to the total amount of the powder mixture.

The present invention also provides an Fe—Co based target material,which is obtainable by the above method, wherein the Fe—Co based targetmaterial is made of an Fe—Co based alloy comprising:

85 to 97 atom % of Fe and Co, which have a Fe:Co weight ratio rangingfrom 8:2 to 2:8; and

3 to 15 atom % of at least one additional element selected from thegroup consisting of Zr, Nb, Ta and Hf.

DETAILED DESCRIPTION OF THE INVENTION Method for Producing Fe—Co BasedTarget Material

First of all, in the method for producing a Fe—Co based target materialaccording to the present invention, a first raw-material powder havingan Fe:Co weight ratio ranging from 8:2 to 7:3 and a second raw-materialpowder having a Fe—Co weight ratio ranging from 2:8 to 0:10 areprepared. As far as the composition of each of the first and secondraw-material powders falls within the above range, the magneticcharacteristics (magnetic permeability) are meaningfully reduced.

Then, the first raw-material powder and the second raw-material powderare mixed together to obtain a powder mixture having a Fe:Co weightratio ranging from 8:2 to 2:8. As far as the weight ratio falls withinthe above range, an increase in magnetic characteristics (magneticpermeability) can be prevented.

In the production method of the present invention, at least oneadditional element selected from the group consisting of Nb, Zr, Ta andHf is added to either one or both of the first and second raw-materialpowders in a total amount of 3 to 15 atom %, desirably, 5 to 10 atom %,with respect to the total amount of the powder mixture. The additionalelement should be added to one or both of the first and secondraw-material powders in advance prior to the mixing. The additionalelement of less than 3 atom % leads to difficulty in amorphization evenif the additional element is added to the Fe—Co powder mixture. Theadditional element of more than 15 atom % leads to a reduced saturationflux density. According to a preferred aspect of the present invention,two additional elements are preferably selected from the groupconsisting of Nb, Zr, Ta and Hf.

According to a preferred aspect of the present invention, it ispreferred that, prior to the mixing step, the additional element isadded to the first raw-material powder in a total amount of not lessthan 1 atom % with respect to the total amount of the first raw-materialpowder, and/or, the additional element is added to the secondraw-material powder in a total amount of not less than 1 atom % withrespect to the total amount of the second raw-material powder. Thismakes it possible to fully achieve the effect of a reduced magneticpermeability provided by the additional element.

The powder mixture thus obtained is consolidated by applying a pressureof not less than 100 MPa, preferably of 100 MPa to 500 MPa, at atemperature of 1073 to 1473 K to obtain a Fe—Co based target material.The consolidating process usable in the method of the present inventionis not particularly limited and may be any process, for example, hotconsolidation such as HIP and hot pressing, as far as the targetmaterial can be consolidated with a high density. The method forproducing powder is not limited to any technique, and includes gasatomizing, water atomizing, and casting-pulverizing. The reason why theconsolidating temperature is selected to the above range is that thedensity of the target material does not reach 100% when theconsolidating temperature is less than 1073 K, and that when it exceeds1473 K the diffusion between particles is extremely promoted so thatplenty of phases having strong magnetic characteristics are formed. Thereason why the consolidating pressure is selected to the above range isthat when the consolidating pressure is less than 100 MPa, the densitydoes not reach 100%. While there is no problem as far as theconsolidating pressure is high, the upper limit of the consolidatingpressure is preferably at 500 MPa from the viewpoint of cost andproductivity.

Fe—Co Based Target Material

The Fe—Co based target material obtainable by the production method ofthe present invention is made of an Fe—Co based alloy comprising 85 to97 atom % of Fe and Co, which have a Fe:Co weight ratio ranging from 8:2to 2:8; and 3 to 15 atom % of at least one additional element selectedfrom the group consisting of Zr, Nb, Ta and Hf. The Fe—Co based targetmaterial thus produced has a high density and a lower magneticpermeability than those of conventional target materials. According to apreferred aspect of the present invention, the Fe—Co based targetmaterial has a magnetic permeability between 10 and 200. As a result,the thickness of the target material can be increased to improveproductivity of thin-films. The magnetic permeability of the targetmaterial of not more than 200 makes it possible to increase thethickness of the target material, while the magnetic permeability of notless than 10 results in satisfactory characteristics as a magneticmaterial.

Sputtering Using Fe—Co Based Target Material

As described above, magnetron sputtering method is generally used forforming soft magnetic films. This magnetron sputtering method is amethod in which a magnet is disposed behind a target material to leakthe magnetic flux onto a surface of the target material for convergingplasma in the leaked magnetic flux region, enabling a high-speedcoating. This magnetron sputtering device has a feature that a magnet isdisposed behind the target material to trap γ electrons in the vicinityof the target material by the application of a magnetic field, aimed atsolving the drawback of bipolar DC glow discharge sputtering devices.Since the γ electron has such an orbit as to be entangled with the linesof magnetic force, the plasma concentrates in the vicinity of the targetmaterial to reduce damages to the substrate. In addition, since themoving distance of the γ electron becomes long, it is possible toperform a high-speed sputtering at a low gas pressure.

EXAMPLES

Examples of the present invention will be in detail explainedhereinafter.

As shown in Table 1, Fe—Co based alloys were produced by gas-atomizingmethods or casting method. The gas-atomizing methods were carried out oncondition that the type of gas was an argon gas, the nozzle diameter was6 mm and the gas pressure was 5 MPa. On the other hand, the castingmethods were carried out by melting the alloys in a ceramic vessel(diameter: 200 mm; length: 30 mm) and then pulverizing the alloys topowders. Powders thus produced were classified into 500 μm or less andeach powder was stirred for one hour by a V-type mixer.

Each powder thus produced was filled in an enclosing vessel made of a SCsteel having a diameter of 200 mm and a height of 100 mm and wasencapsulated with vacuum evacuation at an ultimate vacuum of 10⁻¹ Pa orless, followed by an HIP (hot isostatic pressing) at a temperature of1173K under a pressure of 150 MPa for a holding time of 5 hours. Next,the resultant consolidated bodies were subjected to lathing andwire-cutting to provide final shapes to obtain target materials havingouter diameters of 180 mm and thicknesses of 3 to 10 mm. Properties ofthe above target materials are shown in Table 2. TABLE 1 TotalFormulation After Mixing Additional Raw-Material Powder A Raw-MaterialPowder B Element Com- Additional Com- Additional Composition (at %)position Element position Element Ratio Total of Ratio (at %) Ratio (at%) No. Fe:Co Ratio Zr, Nb, Ta, Hf Fe Co Zr Nb Ta Hf Fe Co Zr Nb Ta Hf 18:2 7   74.2   25.8 4 3 — — — — Examples of 2 7:3 7 71 29 4 3 — — 0 1001 1 Present Invention 3 6:4 7 76 24 4 3 — — 0 100 0 1 4 4:6 7 77 23 — —3 3 0 100 1 0 5 3:7 10 73 27 4 3 — — 0 100 2 1 6 8:2 15 70 30 — 4 5 511   89 0 0 1 7 7:3 14 71 29 6 8 — — 0 100 0 0 8 6:4 12 76 24 6 6 — —11   89 0 0 9 4:6 15 77 23 — — 7 7 9  91 0 1 10 3:7 5 73 27 1 2 — — 13  87 1 1 11 7:3 14 71 29 6 8 — — 0 100 0 0 12 6:4 14 76 24 6 6 — — 11  89 1 1 13 4:6 9 77 23 — — 4 4 9  91 1 0 14 1:8 11 100  0 — 4 5 5 16  84 1 1 1 Comparative 15 9:1 7 73 27 4 3 — — 0 100 0 0 Examples 16 3:716 70 30 8 8 — — 0 100 0 0 17 3:7 16 70 30 — — 8 8 0 100 0 0 18 7:3 1589 11 — 4 5 5 11   89 1 0 19 7:3 10 76 24 — 4 5 5 22   78 1 1 20 3:7 973 27 4 3 — — 0 100 1 1 21 7:3 14 69 31 6 8 — — 0 100 1 1(Underlined part is out of the range of the conditions of the presentinvention)

TABLE 2 Con- solidating Consolidating Magnetic Relative TemperaturePressure Per- Density No. (K) (MPa) meability (%) 1 1173 150 100 100Examples of 2 1173 200 90 100 Present 3 1223 180 85 100 Invention 4 1123220 110 100 5 1223 220 120 100 6 1173 180 100 100 7 1173 200 90 100 81223 220 85 100 9 1123 200 110 100 10 1223 250 120 100 11 1073 200 90100 12 1373 180 85 100 13 1123 200 110 100 14 1223 200 200 100Comparative 15 1223 200 250 100 Examples 16 1223 180 5 100 17 1223 280 5100 18 1223 200 250 100 19 1223 200 220 100 20 1523 200 250 100 21 1023200 240 96(Underlined part is out of the range of the conditions of the presentinvention)

In order to evaluate the characteristics of the target materials thusproduced, the following measurements were carried out.

(1) Magnetic Permeability Measurements

Preparation of ring specimens: outer diameter of 15 mm, inner diameterof 10 mm, height of 5 mm

Apparatus: BH tracer

Applied magnetic field: 8 kA/m

Measurement item: mean magnetic permeability between zero and 100A/m(Oe)

(2) Density

The density measurement was made by the use of Archimedes' principle tocalculate a relative density (ratio of a measured density to acalculated density).

As shown in Table 1, No. 1 to No. 13 are examples of the presentinvention, and No. 14 to No. 21 are comparative examples. In comparativeexample No. 14, the Fe:Co ratio as a whole after the mixing step is 1:8,which indicates a low Fe content and a high Co content, resulting in ahigh magnetic permeability as a magnetic characteristic. In comparativeexample No. 15, the Fe:Co ratio as a whole after the mixing step is 9:1,which indicates a high Fe content and a low Co content, resulting in ahigh magnetic permeability as the magnetic characteristic. Incomparative example No. 16, the content of Zr and Nb as the additionalelements is high, resulting in a low magnetic permeability. Incomparative example No. 17, the content of Ta and Hf as the additionalelements is high, resulting in a low magnetic permeability.

In comparative example No. 18, the first raw-material powder has thehigh Fe ratio and the low Co ratio, resulting in a high magneticpermeability. In comparative example No. 19, the second raw-materialpowder has the low Fe ratio and the high Co ratio, resulting in a highmagnetic permeability. In comparative example No. 20, phases with strongmagnetic characteristics are formed by a reaction due to the highconsolidating temperature, resulting in a high magnetic permeability. Incomparative Example No. 21, the first raw-material powder has the low Feratio and the high Co ratio, resulting in a high magnetic permeability,and the relative density is inferior because of the low consolidatingtemperature.

In contrast, it can be seen that all examples No. 1 to No. 13 of thepresent invention are superior in magnetic permeability as a magneticcharacteristic because examples No. 1 to No. 13 satisfy the conditionsof the present invention.

As described above, a Fe:Co ratio is determined for each of the firstand second raw-material powders, and the total Fe:Co ratio is controlledto fall within an optimum range for the powder mixture to which acertain amount of an additional element is added. This leads to amagnetic permeability as a magnetic characteristic which is lower thanthe conventional one, making it possible to increase the thickness ofthe target material and thus to improve productivity. In consequence,significantly advantageous effects are attained.

1. A method for producing a Fe—Co based target material, comprising thesteps of: preparing a first raw-material powder having an Fe:Co weightratio ranging from 8:2 to 7:3 and a second raw-material powder having anFe—Co weight ratio ranging from 2:8 to 0:10; mixing the firstraw-material powder and the second raw-material powder together toobtain a powder mixture having an Fe:Co weight ratio ranging from 8:2 to2:8; and applying a pressure of not less than 100 MPa to the powdermixture at a temperature ranging from 1073 to 1473 K for consolidation,wherein at least one additional element selected from the groupconsisting of Nb, Zr, Ta and Hf is added to either one or both of thefirst and second raw-material powders in a total amount of 3 to 15 atom% with respect to the total amount of the powder mixture.
 2. The methodaccording to claim 1, wherein, prior to the mixing step, the additionalelement is added to the first raw-material powder in a total amount ofnot less than 1 atom % with respect to the total amount of the firstraw-material powder.
 3. The method according to claim 1 or 2, wherein,prior to the mixing step, the additional element is added to the secondraw-material powder in a total amount of not less than 1 atom % withrespect to the total amount of the second raw-material powder.
 4. AnFe—Co based target material, which is obtainable by the method accordingto claim 1, wherein the Fe—Co based target material is made of an Fe—Cobased alloy comprising: 85 to 97 atom % of Fe and Co, which have a Fe:Coweight ratio ranging from 8:2 to 2:8; and 3 to 15 atom % of at least oneadditional element selected from the group consisting of Zr, Nb, Ta andHf.
 5. The Fe—Co based target material according to claim 4, havingmagnetic permeability ranging from 10 to 200.